Newest Corrosion Weapon: Poison

For those who find blasting and coating too much work to fight corrosion, Australian materials engineers are reporting a new option: arsenic.

In a discovery that could have major implications for multiple transportation and electronics industries, scientists at Monash University have found that adding arsenic to the lightweight metal magnesium dramatically reduces the metal's corrosion rate.

The arsenic acts as a cathodic "poison" that retards the corrosion reaction, says the team, led by Nick Birbilis, an associate professor of materials engineering.

David von Behr / Pixelio

Magnesium alloys are ultra light weight and strong, but vulnerable to rapid corrosion.

The team is working with Australia's national science agency, the Commonwealth Scientific and Industrial Research Organisation (CSIRO), and the University of Wales. Their research, "Poisoning the corrosion of magnesium," has been published in the journal Electrochemistry Communications.

Protecting a Wonder Metal

Magnesium alloy has gained in popularity as a "wonder metal" in the aviation, aerospace, automotive and electronics industries for its ultra light weight (35 percent less than aluminum and 78 percent less than steel) and strength. It is also highly recyclable and shows almost no dimensional change over time due to variations in temperature or vibration.

One of its major downsides, however, has been its vulnerability to rapid corrosion.

“Magnesium products are rapidly evolving to meet the demands industry, but presently are hindered by high corrosion rates," Birbilis says in a research announcement.

The article says the cathodic poisoning resulted in 10 times less hydrogen evolving during corrosion.

Optical micrographs show the contrasting fates of untreated (left) and "poisoned" magnesium (right) after 24 hours of immersion in a salt solution. At right, "a substantial portion of the surface left un-attacked," the authors report.

"To date, no alloying additions to Mg suggest that a reduction in corrosion rate can be imparted," the team's article says. "[H]owever we reveal for the first time that alloying additions of arsenic can impart significant corrosion resistance to Mg via retarding the cathodic reaction."

New Applications

Once available in a more stainless, or corrosion-resistant form, wider magnesium use will lead to significant weight and energy savings in transportation industries, Birbilis said. The arsenic effect is now being trialed as a functional additive to existing commercial alloys, the team says.

“Our breakthrough will help develop the next generation of magnesium products, which must be more stainless,” he said.

Birbilis said the discovery would open the way to more research in creating 'stainless' magnesium products by exploiting other cathodic poisons.

"This is a very important and timely finding," he said. "In an era of light-weighting for energy and emissions reductions, there is a great demand for magnesium alloys in everything from portable electronics to air and land transportation."